This is an automated cherry-pick of pingcap#52208

Signed-off-by: ti-chi-bot <[email protected]>

Author: time-and-fate

build/nogo_config.json

@@ -144,6 +144,11 @@
   },
   "fieldalignment": {
     "exclude_files": {
+<<<<<<< HEAD
+=======
+      "pkg/parser/parser.go": "parser/parser.go code",
+      "pkg/statistics/table.go": "disable this limitation that prevents us from splitting struct fields for clarity",
+>>>>>>> 21e9d3cb40a (planner, statistics: use the correct column ID when recording stats loading status (#52208))
       "external/": "no need to vet third party code",
       ".*_generated\\.go$": "ignore generated code",
       ".*_/testmain\\.go$": "ignore code",

pkg/planner/cardinality/cross_estimation.go

@@ -0,0 +1,312 @@
+// Copyright 2023 PingCAP, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cardinality
+
+import (
+	"math"
+
+	"github.com/pingcap/tidb/pkg/expression"
+	"github.com/pingcap/tidb/pkg/planner/context"
+	"github.com/pingcap/tidb/pkg/planner/property"
+	"github.com/pingcap/tidb/pkg/planner/util"
+	"github.com/pingcap/tidb/pkg/statistics"
+	"github.com/pingcap/tidb/pkg/types"
+	"github.com/pingcap/tidb/pkg/util/ranger"
+	"github.com/pingcap/tidb/pkg/util/set"
+)
+
+// SelectionFactor is the factor which is used to estimate the row count of selection.
+const SelectionFactor = 0.8
+
+// AdjustRowCountForTableScanByLimit will adjust the row count for table scan by limit.
+// For a query like `select pk from t using index(primary) where pk > 10 limit 1`, the row count of the table scan
+// should be adjusted by the limit number 1, because only one row is returned.
+func AdjustRowCountForTableScanByLimit(sctx context.PlanContext,
+	dsStatsInfo, dsTableStats *property.StatsInfo, dsStatisticTable *statistics.Table,
+	path *util.AccessPath, expectedCnt float64, desc bool) float64 {
+	rowCount := path.CountAfterAccess
+	if expectedCnt < dsStatsInfo.RowCount {
+		selectivity := dsStatsInfo.RowCount / path.CountAfterAccess
+		uniformEst := min(path.CountAfterAccess, expectedCnt/selectivity)
+
+		corrEst, ok, corr := crossEstimateTableRowCount(sctx,
+			dsStatsInfo, dsTableStats, dsStatisticTable, path, expectedCnt, desc)
+		if ok {
+			// TODO: actually, before using this count as the estimated row count of table scan, we need additionally
+			// check if count < row_count(first_region | last_region), and use the larger one since we build one copTask
+			// for one region now, so even if it is `limit 1`, we have to scan at least one region in table scan.
+			// Currently, we can use `tikvrpc.CmdDebugGetRegionProperties` interface as `getSampRegionsRowCount()` does
+			// to get the row count in a region, but that result contains MVCC old version rows, so it is not that accurate.
+			// Considering that when this scenario happens, the execution time is close between IndexScan and TableScan,
+			// we do not add this check temporarily.
+
+			// to reduce risks of correlation adjustment, use the maximum between uniformEst and corrEst
+			rowCount = max(uniformEst, corrEst)
+		} else if abs := math.Abs(corr); abs < 1 {
+			correlationFactor := math.Pow(1-abs, float64(sctx.GetSessionVars().CorrelationExpFactor))
+			rowCount = min(path.CountAfterAccess, uniformEst/correlationFactor)
+		}
+	}
+	return rowCount
+}
+
+// crossEstimateTableRowCount estimates row count of table scan using histogram of another column which is in TableFilters
+// and has high order correlation with handle column. For example, if the query is like:
+// `select * from tbl where a = 1 order by pk limit 1`
+// if order of column `a` is strictly correlated with column `pk`, the row count of table scan should be:
+// `1 + row_count(a < 1 or a is null)`
+func crossEstimateTableRowCount(sctx context.PlanContext,
+	dsStatsInfo, dsTableStats *property.StatsInfo, dsStatisticTable *statistics.Table,
+	path *util.AccessPath, expectedCnt float64, desc bool) (float64, bool, float64) {
+	if dsStatisticTable.Pseudo || len(path.TableFilters) == 0 || !sctx.GetSessionVars().EnableCorrelationAdjustment {
+		return 0, false, 0
+	}
+	col, corr := getMostCorrCol4Handle(path.TableFilters, dsStatisticTable, sctx.GetSessionVars().CorrelationThreshold)
+	return crossEstimateRowCount(sctx, dsStatsInfo, dsTableStats, path, path.TableFilters, col, corr, expectedCnt, desc)
+}
+
+// AdjustRowCountForIndexScanByLimit will adjust the row count for table scan by limit.
+// For a query like `select k from t using index(k) where k > 10 limit 1`, the row count of the index scan
+// should be adjusted by the limit number 1, because only one row is returned.
+func AdjustRowCountForIndexScanByLimit(sctx context.PlanContext,
+	dsStatsInfo, dsTableStats *property.StatsInfo, dsStatisticTable *statistics.Table,
+	path *util.AccessPath, expectedCnt float64, desc bool) float64 {
+	rowCount := path.CountAfterAccess
+	count, ok, corr := crossEstimateIndexRowCount(sctx,
+		dsStatsInfo, dsTableStats, dsStatisticTable, path, expectedCnt, desc)
+	if ok {
+		rowCount = count
+	} else if abs := math.Abs(corr); abs < 1 {
+		// If OptOrderingIdxSelRatio is enabled - estimate the difference between index and table filtering, as this represents
+		// the possible scan range when LIMIT rows will be found. orderRatio is the estimated percentage of that range when the first
+		// row is expected to be found. Index filtering applies orderRatio twice. Once found - rows are estimated to be clustered (expectedCnt).
+		// This formula is to bias away from non-filtering (or poorly filtering) indexes that provide order due, where filtering exists
+		// outside of that index. Such plans have high risk since we cannot estimate when rows will be found.
+		orderRatio := sctx.GetSessionVars().OptOrderingIdxSelRatio
+		if dsStatsInfo.RowCount < path.CountAfterAccess && orderRatio >= 0 {
+			rowsToMeetFirst := (((path.CountAfterAccess - path.CountAfterIndex) * orderRatio) + (path.CountAfterIndex - dsStatsInfo.RowCount)) * orderRatio
+			rowCount = rowsToMeetFirst + expectedCnt
+		} else {
+			// Assume rows are linearly distributed throughout the range - for example: selectivity 0.1 assumes that a
+			// qualified row is found every 10th row.
+			correlationFactor := math.Pow(1-abs, float64(sctx.GetSessionVars().CorrelationExpFactor))
+			selectivity := dsStatsInfo.RowCount / rowCount
+			rowCount = min(expectedCnt/selectivity/correlationFactor, rowCount)
+		}
+	}
+	return rowCount
+}
+
+// crossEstimateIndexRowCount estimates row count of index scan using histogram of another column which is in TableFilters/IndexFilters
+// and has high order correlation with the first index column. For example, if the query is like:
+// `select * from tbl where a = 1 order by b limit 1`
+// if order of column `a` is strictly correlated with column `b`, the row count of IndexScan(b) should be:
+// `1 + row_count(a < 1 or a is null)`
+func crossEstimateIndexRowCount(sctx context.PlanContext,
+	dsStatsInfo, dsTableStats *property.StatsInfo, dsStatisticTable *statistics.Table,
+	path *util.AccessPath, expectedCnt float64, desc bool) (float64, bool, float64) {
+	filtersLen := len(path.TableFilters) + len(path.IndexFilters)
+	sessVars := sctx.GetSessionVars()
+	if dsStatisticTable.Pseudo || filtersLen == 0 || !sessVars.EnableExtendedStats || !sctx.GetSessionVars().EnableCorrelationAdjustment {
+		return 0, false, 0
+	}
+	col, corr := getMostCorrCol4Index(path, dsStatisticTable, sessVars.CorrelationThreshold)
+	filters := make([]expression.Expression, 0, filtersLen)
+	filters = append(filters, path.TableFilters...)
+	filters = append(filters, path.IndexFilters...)
+	return crossEstimateRowCount(sctx, dsStatsInfo, dsTableStats, path, filters, col, corr, expectedCnt, desc)
+}
+
+// crossEstimateRowCount is the common logic of crossEstimateTableRowCount and crossEstimateIndexRowCount.
+func crossEstimateRowCount(sctx context.PlanContext,
+	dsStatsInfo, dsTableStats *property.StatsInfo,
+	path *util.AccessPath, conds []expression.Expression, col *expression.Column,
+	corr, expectedCnt float64, desc bool) (float64, bool, float64) {
+	// If the scan is not full range scan, we cannot use histogram of other columns for estimation, because
+	// the histogram reflects value distribution in the whole table level.
+	if col == nil || len(path.AccessConds) > 0 {
+		return 0, false, corr
+	}
+	colUniqueID := col.UniqueID
+	if corr < 0 {
+		desc = !desc
+	}
+	accessConds, remained := ranger.DetachCondsForColumn(sctx, conds, col)
+	if len(accessConds) == 0 {
+		return 0, false, corr
+	}
+	ranges, accessConds, _, err := ranger.BuildColumnRange(accessConds, sctx, col.RetType, types.UnspecifiedLength, sctx.GetSessionVars().RangeMaxSize)
+	if len(ranges) == 0 || len(accessConds) == 0 || err != nil {
+		return 0, err == nil, corr
+	}
+	idxID := int64(-1)
+	idxIDs, idxExists := dsStatsInfo.HistColl.ColUniqueID2IdxIDs[colUniqueID]
+	if idxExists && len(idxIDs) > 0 {
+		idxID = idxIDs[0]
+	}
+	rangeCounts, ok := getColumnRangeCounts(sctx, colUniqueID, ranges, dsTableStats.HistColl, idxID)
+	if !ok {
+		return 0, false, corr
+	}
+	convertedRanges, count, isFull := convertRangeFromExpectedCnt(ranges, rangeCounts, expectedCnt, desc)
+	if isFull {
+		return path.CountAfterAccess, true, 0
+	}
+	var rangeCount float64
+	if idxExists {
+		rangeCount, err = GetRowCountByIndexRanges(sctx, dsTableStats.HistColl, idxID, convertedRanges)
+	} else {
+		rangeCount, err = GetRowCountByColumnRanges(sctx, dsTableStats.HistColl, colUniqueID, convertedRanges)
+	}
+	if err != nil {
+		return 0, false, corr
+	}
+	scanCount := rangeCount + expectedCnt - count
+	if len(remained) > 0 {
+		scanCount = scanCount / SelectionFactor
+	}
+	scanCount = min(scanCount, path.CountAfterAccess)
+	return scanCount, true, 0
+}
+
+// getColumnRangeCounts estimates row count for each range respectively.
+func getColumnRangeCounts(sctx context.PlanContext, colID int64, ranges []*ranger.Range, histColl *statistics.HistColl, idxID int64) ([]float64, bool) {
+	var err error
+	var count float64
+	rangeCounts := make([]float64, len(ranges))
+	for i, ran := range ranges {
+		if idxID >= 0 {
+			idxHist := histColl.Indices[idxID]
+			if statistics.IndexStatsIsInvalid(sctx, idxHist, histColl, idxID) {
+				return nil, false
+			}
+			count, err = GetRowCountByIndexRanges(sctx, histColl, idxID, []*ranger.Range{ran})
+		} else {
+			colHist := histColl.Columns[colID]
+			if statistics.ColumnStatsIsInvalid(colHist, sctx, histColl, colID) {
+				return nil, false
+			}
+			count, err = GetRowCountByColumnRanges(sctx, histColl, colID, []*ranger.Range{ran})
+		}
+		if err != nil {
+			return nil, false
+		}
+		rangeCounts[i] = count
+	}
+	return rangeCounts, true
+}
+
+// convertRangeFromExpectedCnt builds new ranges used to estimate row count we need to scan in table scan before finding specified
+// number of tuples which fall into input ranges.
+func convertRangeFromExpectedCnt(ranges []*ranger.Range, rangeCounts []float64, expectedCnt float64, desc bool) ([]*ranger.Range, float64, bool) {
+	var i int
+	var count float64
+	var convertedRanges []*ranger.Range
+	if desc {
+		for i = len(ranges) - 1; i >= 0; i-- {
+			if count+rangeCounts[i] >= expectedCnt {
+				break
+			}
+			count += rangeCounts[i]
+		}
+		if i < 0 {
+			return nil, 0, true
+		}
+		convertedRanges = []*ranger.Range{{LowVal: ranges[i].HighVal, HighVal: []types.Datum{types.MaxValueDatum()}, LowExclude: !ranges[i].HighExclude, Collators: ranges[i].Collators}}
+	} else {
+		for i = 0; i < len(ranges); i++ {
+			if count+rangeCounts[i] >= expectedCnt {
+				break
+			}
+			count += rangeCounts[i]
+		}
+		if i == len(ranges) {
+			return nil, 0, true
+		}
+		convertedRanges = []*ranger.Range{{LowVal: []types.Datum{{}}, HighVal: ranges[i].LowVal, HighExclude: !ranges[i].LowExclude, Collators: ranges[i].Collators}}
+	}
+	return convertedRanges, count, false
+}
+
+// getMostCorrCol4Index checks if column in the condition is correlated enough with the first index column. If the condition
+// contains multiple columns, return nil and get the max correlation, which would be used in the heuristic estimation.
+func getMostCorrCol4Index(path *util.AccessPath, histColl *statistics.Table, threshold float64) (*expression.Column, float64) {
+	if histColl.ExtendedStats == nil || len(histColl.ExtendedStats.Stats) == 0 {
+		return nil, 0
+	}
+	var cols []*expression.Column
+	cols = expression.ExtractColumnsFromExpressions(cols, path.TableFilters, nil)
+	cols = expression.ExtractColumnsFromExpressions(cols, path.IndexFilters, nil)
+	if len(cols) == 0 {
+		return nil, 0
+	}
+	colSet := set.NewInt64Set()
+	var corr float64
+	var corrCol *expression.Column
+	for _, col := range cols {
+		if colSet.Exist(col.UniqueID) {
+			continue
+		}
+		colSet.Insert(col.UniqueID)
+		curCorr := float64(0)
+		for _, item := range histColl.ExtendedStats.Stats {
+			if (col.ID == item.ColIDs[0] && path.FullIdxCols[0].ID == item.ColIDs[1]) ||
+				(col.ID == item.ColIDs[1] && path.FullIdxCols[0].ID == item.ColIDs[0]) {
+				curCorr = item.ScalarVals
+				break
+			}
+		}
+		if corrCol == nil || math.Abs(corr) < math.Abs(curCorr) {
+			corrCol = col
+			corr = curCorr
+		}
+	}
+	if len(colSet) == 1 && math.Abs(corr) >= threshold {
+		return corrCol, corr
+	}
+	return nil, corr
+}
+
+// getMostCorrCol4Handle checks if column in the condition is correlated enough with handle. If the condition
+// contains multiple columns, return nil and get the max correlation, which would be used in the heuristic estimation.
+func getMostCorrCol4Handle(exprs []expression.Expression, histColl *statistics.Table, threshold float64) (*expression.Column, float64) {
+	var cols []*expression.Column
+	cols = expression.ExtractColumnsFromExpressions(cols, exprs, nil)
+	if len(cols) == 0 {
+		return nil, 0
+	}
+	colSet := set.NewInt64Set()
+	var corr float64
+	var corrCol *expression.Column
+	for _, col := range cols {
+		if colSet.Exist(col.UniqueID) {
+			continue
+		}
+		colSet.Insert(col.UniqueID)
+		hist, ok := histColl.Columns[col.ID]
+		if !ok {
+			continue
+		}
+		curCorr := hist.Correlation
+		if corrCol == nil || math.Abs(corr) < math.Abs(curCorr) {
+			corrCol = col
+			corr = curCorr
+		}
+	}
+	if len(colSet) == 1 && math.Abs(corr) >= threshold {
+		return corrCol, corr
+	}
+	return nil, corr
+}